There is a large need in a multiple of industries (from chemical production to pharmaceutical development), chemical and biological research, and diagnostics to perform thermally-driven chemical reactions. Typically, thermally-driven chemical reactions are performed in reaction vessels with separate heater elements that are in direct contact with the vessel. The vessel can be glass, metal, ceramic, or plastic. The vessel can also be for one-time use, or disposable. Heating a sample within the vessel requires the use of a heater. However, such a heater is not typically integrated into a disposable vessel an integrated heater is too expensive to mass produce and be disposable after one-time use.
The polymerase chain reaction (PCR) is a technique for the amplification of nucleic acids, such as RNA and DNA, in the laboratory. PCR is a common method of creating copies of specific fragments of DNA. PCR rapidly amplifies a single DNA molecule into many billions of molecules. In one application of the technology, small samples of DNA, such as those found in a strand of hair at a crime scene, can produce sufficient copies to carry out forensic tests.
PCR is typically performed using thermal cycling in which a sample is subjected to a series of heating and cooling steps. Conventional PCR instruments include a PCR tube for holding the sample and a heater coupled to the PCR tube. There are other methods of amplifying nucleic acids, which involve isothermal (a constant temperature) temperature rather than thermal cycling as.
The conventional design approach for PCR tubes and heaters is to use silicon, ceramic or other thermally superior but relatively expensive materials. These PCR tubes and heaters are not disposable after use and, therefore, need to be integrated as part of the instrument. Under these constraints, the PCR instrument design options include either leaving the PCR tubes in the heaters as part of the instrument and having a sample delivery mechanism interface with it fluidically each time, or using a contact-based heater design approach for each PCR tube to snap in place each time a new PCR tube is inserted, or using hot air/cool air for thermal cycling.
Disadvantages exist for each of these options. Leaving the tube in the heater for repeated thermal cycling eventually leads to material degradation due to thermal fatigue and is not advisable. Further, a fluidic connection between the sample delivery mechanism and the PCR plastic tubes requires a complex sealing interface design which can lead to contamination issues between each run. In some cases, an operator manually delivers the sample into the PCR tubes. This is manually intensive and does not lend itself to automated applications.
Design of a contact-based heater approach is quite challenging and has drawbacks such as achieving uniform tangential coverage for heating of the tubes and the sample contained therein. Also, there are issues such as tube alignment and registration for establishing a repeatable and acceptable interface between the tubing and heater each time a new PCR tube is inserted. Additionally, contact-based heaters must be robust enough to withstand repeated use. To provide this robustness requires a greater mass, both physical mass and thermal mass. A larger physical mass adds to the overall weight and size of the heater, which is not desirable. An increased thermal mass reduces the efficiency and response time of the heater.
Using the hot air/cool air approach for thermal cycling is not energy-efficient. Additionally, the hot air/cool air approach has a slower response time than direct contact approaches, the system is more bulky, and oftentimes more noisy.
Heaters used to heat PCR tubes are basically sleeves with a hole in the center through which the tube is inserted. The tube can either be permanently fixed in place within the heater or the tube can be removed from the heater and replaced with a new tube for each new sample to be heated. In the case where the tube is permanently fixed within the heater, the issue of creating the proper contact between the tube and the heater is eliminated, but this creates the problem of properly mating the tube to a sample delivery mechanism for repeated connections and disconnections. Further, the issue of cross-contamination is raised when reusing the same tube for different samples.
In the case where the tube is replaced for each new sample, it is necessary to thread the tube through the sleeve each time the tube is replaced. The problem is creating a repeatable contact between the tube and the heater with each newly introduced tube.
There is a need for a heater and tube assembly that effectively and efficiently provides a fluidic connection to the tube for delivering a sample, and provides a properly configured thermal interface between the tube and the heater.